Experimental investigation on solubility of CO2 in two dipentaerythritol esters

doi:10.11949/0438-1157.20251179

Abstract

Abstract:

CO₂ is considered as a replacement refrigerant in automotive air conditioning due to its extremely low global warming potential (GWP=1) and ozone depletion potential (ODP=0). The phase equilibrium (solubility) between CO₂ and lubricants is essential for the design and optimization of refrigeration system. To elucidate the CO₂ absorption capacity of individual components in polyol ester (POE) lubricants, the solubility of CO₂ in dipentaerythritol hexapentanoate (DiPEC5) and dipentaerythritol hexahydroxystearate (DiPEC7) were determined via the isobaric saturation method. The temperature range for the present measurements was 283.15 K to 343.15 K. Experimental data were correlated using SRK equation combined with the modified van der Waals-Berthelot mixing rule. Results showed that the average absolute relative deviations between the experimental pressure and calculated values for CO₂/DiPEC5 and CO₂/DiPEC7 systems are 1.73% and 2.25%, respectively. And the corresponding maximum absolute relative deviations are 7.90% and 7.82%. Furthermore, the solubilities between CO₂ and various pure components in polyol ester lubricants (linear pentaerythritol ester PEC, branched pentaerythritol ester PEBM, and linear dipentaerythritol ester DiPEC) were compared and analyzed. Results revealed that the solubility of CO₂ dissolved in DiPEC is significantly higher than that of PEC and PEBM. This work provides fundamental physical property data for the further development of novel lubricants.

Key words: carbon dioxide, solubility, dipentaerythritol ester, equation of state

摘要：

CO₂因其极低的全球变暖潜能（GWP=1）和臭氧消耗潜能（ODP=0）而被认为是汽车空调领域的替代制冷剂，而CO₂与润滑油的相平衡（溶解度）是制冷系统设计、优化所必需的基础物性。为了查明POE类润滑油中各组分对CO₂的吸收能力，采用等体积饱和法测量了CO₂在两种POE润滑油纯组分即双季戊四醇六戊酸酯（DiPEC5）和双季戊四醇六庚酸酯（DiPEC7）中的溶解度，测量的温度范围为283.15 K-343.15 K。使用SRK方程并结合修正的van der Waals-Berthelot混合法则对实验数据进行了关联。结果表明，CO₂/DiPEC5和CO₂/DiPEC7体系的实验平衡压力和模型计算值之间的平均绝对相对偏差分别为1.73%和2.25%，最大相对偏差分别为7.90%和7.82%。此外，还对比分析了CO₂在POE润滑油不同纯组分（直链季戊四醇酯PEC、支链季戊四醇酯PEBM以及直链双季戊四醇酯DiPEC）中的溶解度，发现CO₂在DiPEC中的溶解度显著高于PEC和PEBM。本文工作为进一步研发新型的润滑油提供了基础的物性数据。

关键词: 二氧化碳, 溶解性, 双季戊四醇酯, 状态方程

CLC Number:

TQ 028.8

Chenhan CHI, Wenzhe DANG, Xiaopo WANG. Experimental investigation on solubility of CO₂ in two dipentaerythritol esters[J]. CIESC Journal, DOI: 10.11949/0438-1157.20251179.

池琛晗, 党文喆, 王晓坡. CO₂在双季戊四醇酯中的溶解度实验研究[J]. 化工学报, DOI: 10.11949/0438-1157.20251179.

Figures/Tables 14

Fig. 1 Chemical structures of DiPEC5 and DiPEC7

Fig. 2 Schematic diagram of the experimental setup based on isobaric saturation method

Table 1 Measurement uncertainty of CO2 solubility

不确定度来源	数值
u(V_gasc )	0.02 cm³
u(V_equic )	0.02 cm³
u(V_oil )	0.003 cm³
u(ρ₁)	1.6×10^-5 g·cm^-3
$u ρ 1, l d 1$	6×10^-5 g·cm^-3
u(m₂)	10^-4 g
压力传感器	2 kPa
铂电阻温度计	0.03 K
整体拓展不确定度	<3.5%

Table 1 Measurement uncertainty of CO2 solubility

不确定度来源	数值
u(V_gasc )	0.02 cm³
u(V_equic )	0.02 cm³
u(V_oil )	0.003 cm³
u(ρ₁)	1.6×10^-5 g·cm^-3
$u ρ 1, l d 1$	6×10^-5 g·cm^-3
u(m₂)	10^-4 g
压力传感器	2 kPa
铂电阻温度计	0.03 K
整体拓展不确定度	<3.5%

Table 2 Experimental solubility data on CO₂ dissolved in DiPEC5

p/MPa	x₁	p/MPa	x₁	p/MPa	x₁	p/MPa	x₁
283.15 K		293.15 K		303.15 K		313.15 K
0.123	0.107	0.130	0.092	0.135	0.082	0.141	0.075
0.321	0.236	0.337	0.211	0.353	0.191	0.368	0.174
0.544	0.347	0.572	0.315	0.598	0.289	0.624	0.266
0.769	0.446	0.809	0.412	0.848	0.384	0.885	0.358
0.990	0.530	1.046	0.489	1.097	0.461	1.146	0.434
1.211	0.599	1.282	0.559	1.347	0.530	1.410	0.502
1.423	0.658	1.512	0.615	1.595	0.589	1.667	0.563
323.15 K		333.15 K		343.15 K
0.146	0.068	0.152	0.061	0.157	0.056
0.382	0.159	0.396	0.148	0.410	0.137
0.649	0.246	0.673	0.231	0.697	0.217
0.921	0.336	0.956	0.318	0.992	0.298
1.194	0.412	1.242	0.389	1.288	0.371
1.471	0.478	1.532	0.454	1.590	0.436
1.743	0.533	1.817	0.508	1.888	0.492

Fig. 3 Variation of CO2 solubility with equilibrium pressure in CO2/DiPEC5 system

Fig. 4 Variation of CO2 solubility with equilibrium pressure in CO2/DiPEC7 mixture

Table 3 Experimental solubility data on CO₂ dissolved in DiPEC7

p/MPa	x₁	p/MPa	x₁	p/MPa	x₁	p/MPa	x₁
283.15 K		293.15 K		303.15 K		313.15 K
0.126	0.116	0.132	0.103	0.137	0.093	0.143	0.083
0.325	0.250	0.340	0.225	0.354	0.208	0.369	0.189
0.535	0.360	0.560	0.333	0.585	0.306	0.610	0.282
0.764	0.457	0.802	0.422	0.839	0.395	0.875	0.367
0.992	0.529	1.042	0.496	1.091	0.467	1.138	0.437
1.209	0.589	1.273	0.555	1.334	0.526	1.393	0.497
1.423	0.644	1.501	0.611	1.575	0.585	1.647	0.556
323.15 K		333.15 K		343.15 K
0.148	0.076	0.154	0.069	0.159	0.064
0.383	0.174	0.397	0.162	0.411	0.152
0.633	0.263	0.657	0.246	0.680	0.232
0.910	0.344	0.944	0.327	0.977	0.311
1.185	0.414	1.231	0.393	1.275	0.376
1.451	0.476	1.508	0.455	1.564	0.438
1.718	0.533	1.787	0.514	1.855	0.497

Table 4 Values of coefficient βk in the formula

物质名称	β₀	β₁	β₂	β₃
CO₂	1.0005	0.43866	-0.10498	-0.6250
DiPEC	1.0	1.0	0.0	0.0

Table 5 Correlation results of the binary interaction parameters for CO2/dipentaerythritol ester mixture

参数名称	CO₂+DiPEC5	CO₂+DiPEC7
l_ij	3.56✕10^-2	-1.15✕10^-2
l_ji	3.55✕10^-2	-1.93✕10^-2
m_ij	-2.26✕10^-2	3.66✕10^-2
τ_0,_ij	4.77✕10^-2	1.32✕10^-1
τ_1,_ij	97.18	64.36
τ_2,_ij	2.694✕10^-1	2.513✕10^-3
AARD/%	1.73	2.25
MARD/%	7.90	7.82

Fig. 5 Deviation between equilibrium pressure and calculated results for CO2/DiPEC5 system

Fig. 6 Deviation between equilibrium pressure and calculated results for CO2/DiPEC7 system

Fig. 7 Solubility comparison of CO2 in DiPEC5 or DiPEC7

Fig. 8 Solubility comparison of CO2 in PEC5, PEBM5, and DiPEC5

Fig. 9 Solubility comparison of CO2 in different pentaerythritol ester at 283.15 K

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Experimental investigation on solubility of CO₂ in two dipentaerythritol esters

CO₂在双季戊四醇酯中的溶解度实验研究

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